x+y=3π/4,则(1-tanx)(1-tany)

(1-tanx)(1-tany)=1-(tanx+tany)+tanxtany.(1)因为x+y=3π/4而且tan(x+y)=(tanx+tany)/(1-tanxtany)tan(x+y)=tan(3π/4)=-1(tanx+tany)/(1-tanxtany)=-1tanx+tany=tanxtany-1.(2)将(2)式子代入(1)式子得(1-tanx)(1-t...